Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $155.48   13.869%   $177.0435   $177.04   $177.05   $177.00  
  Purchase #2 $240.98   11.398%   $268.4469   $268.45   $268.45   $268.40  
  Purchase #3 $127.76   3.829%   $132.6519   $132.65   $132.65   $132.70  
  Purchase #4 $120.52   13.681%   $137.0083   $137.01   $137.00   $137.00  
  Purchase #5 $181.57   12.116%   $203.569   $203.57   $203.55   $203.60  
  Purchase #6 $163.93   3.794%   $170.1495   $170.15   $170.15   $170.10  
  Purchase #7 $240.87   6.688%   $256.9794   $256.98   $257.00   $257.00  
  7 purchase totals = $1,231.11       $1,345.8485   $1,345.85   $1,345.85   $1,345.80