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 $23.44   6.520%   $24.9683   $24.97   $24.95   $25.00  
  Purchase #2 $32.82   7.706%   $35.3491   $35.35   $35.35   $35.30  
  Purchase #3 $214.67   5.303%   $226.054   $226.05   $226.05   $226.10  
  Purchase #4 $59.41   3.837%   $61.6896   $61.69   $61.70   $61.70  
  Purchase #5 $217.74   9.769%   $239.011   $239.01   $239.00   $239.00  
  Purchase #6 $181.73   11.322%   $202.3055   $202.31   $202.30   $202.30  
  Purchase #7 $87.78   4.369%   $91.6151   $91.62   $91.60   $91.60  
  7 purchase totals = $817.59       $880.9926   $881.00   $880.95   $881.00