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 $90.42   3.176%   $93.2917   $93.29   $93.30   $93.30  
  Purchase #2 $222.58   5.667%   $235.1936   $235.19   $235.20   $235.20  
  Purchase #3 $43.96   11.150%   $48.8615   $48.86   $48.85   $48.90  
  Purchase #4 $195.97   12.383%   $220.237   $220.24   $220.25   $220.20  
  Purchase #5 $156.90   13.645%   $178.309   $178.31   $178.30   $178.30  
  Purchase #6 $213.33   9.136%   $232.8198   $232.82   $232.80   $232.80  
  Purchase #7 $193.88   5.198%   $203.9579   $203.96   $203.95   $204.00  
  7 purchase totals = $1,117.04       $1,212.6705   $1,212.67   $1,212.65   $1,212.70