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 $62.57   7.159%   $67.0494   $67.05   $67.05   $67.00  
  Purchase #2 $212.29   7.554%   $228.3264   $228.33   $228.35   $228.30  
  Purchase #3 $68.32   10.210%   $75.2955   $75.30   $75.30   $75.30  
  Purchase #4 $53.71   3.639%   $55.6645   $55.66   $55.65   $55.70  
  Purchase #5 $123.70   11.793%   $138.2879   $138.29   $138.30   $138.30  
  Purchase #6 $51.87   5.189%   $54.5615   $54.56   $54.55   $54.60  
  Purchase #7 $71.39   12.581%   $80.3716   $80.37   $80.35   $80.40  
  7 purchase totals = $643.85       $699.5568   $699.56   $699.55   $699.60