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 $58.71   8.355%   $63.6152   $63.62   $63.60   $63.60  
  Purchase #2 $139.30   7.451%   $149.6792   $149.68   $149.70   $149.70  
  Purchase #3 $65.29   4.619%   $68.3057   $68.31   $68.30   $68.30  
  Purchase #4 $106.33   12.634%   $119.7637   $119.76   $119.75   $119.80  
  Purchase #5 $233.93   8.715%   $254.317   $254.32   $254.30   $254.30  
  Purchase #6 $191.74   6.649%   $204.4888   $204.49   $204.50   $204.50  
  Purchase #7 $181.95   11.127%   $202.1956   $202.20   $202.20   $202.20  
  7 purchase totals = $977.25       $1,062.3652   $1,062.38   $1,062.35   $1,062.40