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 $34.48   5.516%   $36.3819   $36.38   $36.40   $36.40  
  Purchase #2 $215.94   12.536%   $243.0102   $243.01   $243.00   $243.00  
  Purchase #3 $218.93   4.353%   $228.46   $228.46   $228.45   $228.50  
  Purchase #4 $54.47   13.304%   $61.7167   $61.72   $61.70   $61.70  
  Purchase #5 $165.95   7.486%   $178.373   $178.37   $178.35   $178.40  
  Purchase #6 $165.55   8.658%   $179.8833   $179.88   $179.90   $179.90  
  Purchase #7 $88.99   4.429%   $92.9314   $92.93   $92.95   $92.90  
  7 purchase totals = $944.31       $1,020.7565   $1,020.75   $1,020.75   $1,020.80