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 $234.97   8.366%   $254.6276   $254.63   $254.65   $254.60  
  Purchase #2 $110.68   8.594%   $120.1918   $120.19   $120.20   $120.20  
  Purchase #3 $136.79   12.585%   $154.005   $154.01   $154.00   $154.00  
  Purchase #4 $99.53   9.337%   $108.8231   $108.82   $108.80   $108.80  
  Purchase #5 $247.46   11.523%   $275.9748   $275.97   $275.95   $276.00  
  Purchase #6 $228.49   6.575%   $243.5132   $243.51   $243.50   $243.50  
  Purchase #7 $181.30   7.807%   $195.4541   $195.45   $195.45   $195.50  
  7 purchase totals = $1,239.22       $1,352.5896   $1,352.58   $1,352.55   $1,352.60