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 $174.59   9.403%   $191.0067   $191.01   $191.00   $191.00  
  Purchase #2 $157.25   4.143%   $163.7649   $163.76   $163.75   $163.80  
  Purchase #3 $106.37   11.853%   $118.978   $118.98   $119.00   $119.00  
  Purchase #4 $233.60   4.277%   $243.5911   $243.59   $243.60   $243.60  
  Purchase #5 $91.28   9.146%   $99.6285   $99.63   $99.65   $99.60  
  Purchase #6 $21.34   12.855%   $24.0833   $24.08   $24.10   $24.10  
  Purchase #7 $122.85   5.837%   $130.0208   $130.02   $130.00   $130.00  
  7 purchase totals = $907.28       $971.0733   $971.07   $971.10   $971.10