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 $49.59   9.526%   $54.3139   $54.31   $54.30   $54.30  
  Purchase #2 $157.56   11.393%   $175.5108   $175.51   $175.50   $175.50  
  Purchase #3 $231.85   8.263%   $251.0078   $251.01   $251.00   $251.00  
  Purchase #4 $227.91   7.751%   $245.5753   $245.58   $245.60   $245.60  
  Purchase #5 $94.53   9.416%   $103.4309   $103.43   $103.45   $103.40  
  Purchase #6 $5.94   10.455%   $6.561   $6.56   $6.55   $6.60  
  Purchase #7 $85.68   12.221%   $96.151   $96.15   $96.15   $96.20  
  7 purchase totals = $853.06       $932.5507   $932.55   $932.55   $932.60