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 $192.59   13.814%   $219.1944   $219.19   $219.20   $219.20  
  Purchase #2 $202.58   11.484%   $225.8443   $225.84   $225.85   $225.80  
  Purchase #3 $48.38   6.683%   $51.6132   $51.61   $51.60   $51.60  
  Purchase #4 $170.70   11.775%   $190.7999   $190.80   $190.80   $190.80  
  Purchase #5 $56.91   7.312%   $61.0713   $61.07   $61.05   $61.10  
  Purchase #6 $167.30   7.864%   $180.4565   $180.46   $180.45   $180.50  
  Purchase #7 $19.87   10.748%   $22.0056   $22.01   $22.00   $22.00  
  7 purchase totals = $858.33       $950.9852   $950.98   $950.95   $951.00