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 $232.46   9.179%   $253.7975   $253.80   $253.80   $253.80  
  Purchase #2 $189.48   12.611%   $213.3753   $213.38   $213.40   $213.40  
  Purchase #3 $246.52   7.482%   $264.9646   $264.96   $264.95   $265.00  
  Purchase #4 $75.87   6.315%   $80.6612   $80.66   $80.65   $80.70  
  Purchase #5 $150.25   9.213%   $164.0925   $164.09   $164.10   $164.10  
  Purchase #6 $125.78   4.592%   $131.5558   $131.56   $131.55   $131.60  
  Purchase #7 $71.34   3.152%   $73.5886   $73.59   $73.60   $73.60  
  7 purchase totals = $1,091.70       $1,182.0355   $1,182.04   $1,182.05   $1,182.20