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 $53.85   11.343%   $59.9582   $59.96   $59.95   $60.00  
  Purchase #2 $224.87   6.251%   $238.9266   $238.93   $238.95   $238.90  
  Purchase #3 $131.77   8.385%   $142.8189   $142.82   $142.80   $142.80  
  Purchase #4 $181.76   3.363%   $187.8726   $187.87   $187.85   $187.90  
  Purchase #5 $95.25   8.185%   $103.0462   $103.05   $103.05   $103.00  
  Purchase #6 $70.45   3.729%   $73.0771   $73.08   $73.10   $73.10  
  Purchase #7 $123.59   9.485%   $135.3125   $135.31   $135.30   $135.30  
  7 purchase totals = $881.54       $941.0121   $941.02   $941.00   $941.00