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 $54.29   6.699%   $57.9269   $57.93   $57.95   $57.90  
  Purchase #2 $187.79   8.106%   $203.0123   $203.01   $203.00   $203.00  
  Purchase #3 $154.83   7.628%   $166.6404   $166.64   $166.65   $166.60  
  Purchase #4 $30.40   5.563%   $32.0912   $32.09   $32.10   $32.10  
  Purchase #5 $52.97   13.518%   $60.1305   $60.13   $60.15   $60.10  
  Purchase #6 $175.89   11.870%   $196.7681   $196.77   $196.75   $196.80  
  Purchase #7 $218.81   9.140%   $238.8092   $238.81   $238.80   $238.80  
  7 purchase totals = $874.98       $955.3786   $955.38   $955.40   $955.30