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 $172.35   13.378%   $195.407   $195.41   $195.40   $195.40  
  Purchase #2 $191.56   9.194%   $209.172   $209.17   $209.15   $209.20  
  Purchase #3 $204.88   10.665%   $226.7305   $226.73   $226.75   $226.70  
  Purchase #4 $77.52   12.308%   $87.0612   $87.06   $87.05   $87.10  
  Purchase #5 $101.75   8.600%   $110.5005   $110.50   $110.50   $110.50  
  Purchase #6 $139.59   11.551%   $155.714   $155.71   $155.70   $155.70  
  Purchase #7 $73.32   13.286%   $83.0613   $83.06   $83.05   $83.10  
  7 purchase totals = $960.97       $1,067.6465   $1,067.64   $1,067.60   $1,067.70