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 $149.77   7.662%   $161.2454   $161.25   $161.25   $161.20  
  Purchase #2 $41.74   8.201%   $45.1631   $45.16   $45.15   $45.20  
  Purchase #3 $190.29   11.771%   $212.689   $212.69   $212.70   $212.70  
  Purchase #4 $77.56   7.262%   $83.1924   $83.19   $83.20   $83.20  
  Purchase #5 $56.25   3.264%   $58.086   $58.09   $58.10   $58.10  
  Purchase #6 $244.39   9.519%   $267.6535   $267.65   $267.65   $267.70  
  Purchase #7 $180.94   7.669%   $194.8163   $194.82   $194.80   $194.80  
  7 purchase totals = $940.94       $1,022.8457   $1,022.85   $1,022.85   $1,022.90