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 $67.75   11.674%   $75.6591   $75.66   $75.65   $75.70  
  Purchase #2 $109.62   12.480%   $123.3006   $123.30   $123.30   $123.30  
  Purchase #3 $227.71   6.549%   $242.6227   $242.62   $242.60   $242.60  
  Purchase #4 $84.52   4.748%   $88.533   $88.53   $88.55   $88.50  
  Purchase #5 $170.43   7.711%   $183.5719   $183.57   $183.55   $183.60  
  Purchase #6 $241.57   9.606%   $264.7752   $264.78   $264.80   $264.80  
  Purchase #7 $158.81   9.658%   $174.1479   $174.15   $174.15   $174.10  
  7 purchase totals = $1,060.41       $1,152.6104   $1,152.61   $1,152.60   $1,152.60