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 $182.78   8.679%   $198.6435   $198.64   $198.65   $198.60  
  Purchase #2 $165.63   13.243%   $187.5644   $187.56   $187.55   $187.60  
  Purchase #3 $67.55   13.465%   $76.6456   $76.65   $76.65   $76.60  
  Purchase #4 $87.28   5.780%   $92.3248   $92.32   $92.30   $92.30  
  Purchase #5 $16.57   6.151%   $17.5892   $17.59   $17.60   $17.60  
  Purchase #6 $23.52   6.339%   $25.0109   $25.01   $25.00   $25.00  
  Purchase #7 $133.81   11.559%   $149.2771   $149.28   $149.30   $149.30  
  7 purchase totals = $677.14       $747.0555   $747.05   $747.05   $747.00