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 $35.71   6.656%   $38.0869   $38.09   $38.10   $38.10  
  Purchase #2 $126.78   5.436%   $133.6718   $133.67   $133.65   $133.70  
  Purchase #3 $29.52   5.459%   $31.1315   $31.13   $31.15   $31.10  
  Purchase #4 $173.82   13.159%   $196.693   $196.69   $196.70   $196.70  
  Purchase #5 $68.56   11.350%   $76.3416   $76.34   $76.35   $76.30  
  Purchase #6 $15.25   9.467%   $16.6937   $16.69   $16.70   $16.70  
  Purchase #7 $66.81   12.349%   $75.0604   $75.06   $75.05   $75.10  
  7 purchase totals = $516.45       $567.6789   $567.67   $567.70   $567.70