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 $120.48   13.496%   $136.74   $136.74   $136.75   $136.70  
  Purchase #2 $22.37   11.712%   $24.99   $24.99   $25.00   $25.00  
  Purchase #3 $147.95   8.386%   $160.3571   $160.36   $160.35   $160.40  
  Purchase #4 $87.99   6.831%   $94.0006   $94.00   $94.00   $94.00  
  Purchase #5 $202.25   12.451%   $227.4321   $227.43   $227.45   $227.40  
  Purchase #6 $234.89   5.440%   $247.668   $247.67   $247.65   $247.70  
  Purchase #7 $136.26   10.662%   $150.788   $150.79   $150.80   $150.80  
  7 purchase totals = $952.19       $1,041.9758   $1,041.98   $1,042.00   $1,042.00