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 $187.26   3.504%   $193.8216   $193.82   $193.80   $193.80  
  Purchase #2 $54.82   5.179%   $57.6591   $57.66   $57.65   $57.70  
  Purchase #3 $174.34   5.649%   $184.1885   $184.19   $184.20   $184.20  
  Purchase #4 $148.56   12.134%   $166.5863   $166.59   $166.60   $166.60  
  Purchase #5 $213.51   13.797%   $242.968   $242.97   $242.95   $243.00  
  Purchase #6 $207.41   9.369%   $226.8422   $226.84   $226.85   $226.80  
  Purchase #7 $238.65   6.392%   $253.9045   $253.90   $253.90   $253.90  
  7 purchase totals = $1,224.55       $1,325.9702   $1,325.97   $1,325.95   $1,326.00