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 $59.84   4.789%   $62.7057   $62.71   $62.70   $62.70  
  Purchase #2 $136.79   10.519%   $151.1789   $151.18   $151.20   $151.20  
  Purchase #3 $250.64   9.758%   $275.0975   $275.10   $275.10   $275.10  
  Purchase #4 $249.70   4.157%   $260.08   $260.08   $260.10   $260.10  
  Purchase #5 $212.47   6.551%   $226.3889   $226.39   $226.40   $226.40  
  Purchase #6 $79.48   10.778%   $88.0464   $88.05   $88.05   $88.00  
  Purchase #7 $67.97   10.702%   $75.2441   $75.24   $75.25   $75.20  
  7 purchase totals = $1,056.89       $1,138.7415   $1,138.75   $1,138.80   $1,138.70