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 $241.59   7.704%   $260.2021   $260.20   $260.20   $260.20  
  Purchase #2 $43.62   5.702%   $46.1072   $46.11   $46.10   $46.10  
  Purchase #3 $134.98   8.377%   $146.2873   $146.29   $146.30   $146.30  
  Purchase #4 $5.39   7.199%   $5.778   $5.78   $5.80   $5.80  
  Purchase #5 $220.59   5.855%   $233.5055   $233.51   $233.50   $233.50  
  Purchase #6 $75.60   11.279%   $84.1269   $84.13   $84.15   $84.10  
  Purchase #7 $70.80   8.809%   $77.0368   $77.04   $77.05   $77.00  
  7 purchase totals = $792.57       $853.0438   $853.06   $853.10   $853.00