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 $197.60   8.809%   $215.0066   $215.01   $215.00   $215.00  
  Purchase #2 $134.80   9.765%   $147.9632   $147.96   $147.95   $148.00  
  Purchase #3 $93.59   13.857%   $106.5588   $106.56   $106.55   $106.60  
  Purchase #4 $54.88   9.300%   $59.9838   $59.98   $60.00   $60.00  
  Purchase #5 $135.35   5.370%   $142.6183   $142.62   $142.60   $142.60  
  Purchase #6 $247.33   11.528%   $275.8422   $275.84   $275.85   $275.80  
  Purchase #7 $38.57   12.784%   $43.5008   $43.50   $43.50   $43.50  
  7 purchase totals = $902.12       $991.4737   $991.47   $991.45   $991.50