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 $34.67   9.441%   $37.9432   $37.94   $37.95   $37.90  
  Purchase #2 $202.91   9.241%   $221.6609   $221.66   $221.65   $221.70  
  Purchase #3 $167.75   13.604%   $190.5707   $190.57   $190.55   $190.60  
  Purchase #4 $203.44   4.739%   $213.081   $213.08   $213.10   $213.10  
  Purchase #5 $180.33   12.519%   $202.9055   $202.91   $202.90   $202.90  
  Purchase #6 $232.72   11.870%   $260.3439   $260.34   $260.35   $260.30  
  Purchase #7 $93.90   11.560%   $104.7548   $104.75   $104.75   $104.80  
  7 purchase totals = $1,115.72       $1,231.2600   $1,231.25   $1,231.25   $1,231.30