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 $117.69   8.583%   $127.7913   $127.79   $127.80   $127.80  
  Purchase #2 $151.95   12.336%   $170.6946   $170.69   $170.70   $170.70  
  Purchase #3 $23.52   9.386%   $25.7276   $25.73   $25.75   $25.70  
  Purchase #4 $227.97   11.670%   $254.5741   $254.57   $254.55   $254.60  
  Purchase #5 $227.98   11.447%   $254.0769   $254.08   $254.10   $254.10  
  Purchase #6 $97.47   10.147%   $107.3603   $107.36   $107.35   $107.40  
  Purchase #7 $231.93   13.570%   $263.4029   $263.40   $263.40   $263.40  
  7 purchase totals = $1,078.51       $1,203.6277   $1,203.62   $1,203.65   $1,203.70