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 $92.31   10.458%   $101.9638   $101.96   $101.95   $102.00  
  Purchase #2 $23.91   3.566%   $24.7626   $24.76   $24.75   $24.80  
  Purchase #3 $141.25   5.720%   $149.3295   $149.33   $149.35   $149.30  
  Purchase #4 $132.74   11.175%   $147.5737   $147.57   $147.55   $147.60  
  Purchase #5 $155.52   9.690%   $170.5899   $170.59   $170.60   $170.60  
  Purchase #6 $212.77   5.139%   $223.7043   $223.70   $223.70   $223.70  
  Purchase #7 $127.96   3.152%   $131.9933   $131.99   $132.00   $132.00  
  7 purchase totals = $886.46       $949.9171   $949.90   $949.90   $950.00