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 $53.82   7.111%   $57.6471   $57.65   $57.65   $57.60  
  Purchase #2 $138.79   13.869%   $158.0388   $158.04   $158.05   $158.00  
  Purchase #3 $59.60   10.225%   $65.6941   $65.69   $65.70   $65.70  
  Purchase #4 $23.84   8.841%   $25.9477   $25.95   $25.95   $25.90  
  Purchase #5 $186.45   6.773%   $199.0783   $199.08   $199.10   $199.10  
  Purchase #6 $175.64   5.300%   $184.9489   $184.95   $184.95   $184.90  
  Purchase #7 $173.95   4.333%   $181.4873   $181.49   $181.50   $181.50  
  7 purchase totals = $812.09       $872.8422   $872.85   $872.90   $872.70