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 $241.92   13.709%   $275.0848   $275.08   $275.10   $275.10  
  Purchase #2 $110.69   6.322%   $117.6878   $117.69   $117.70   $117.70  
  Purchase #3 $65.47   4.374%   $68.3337   $68.33   $68.35   $68.30  
  Purchase #4 $121.77   5.348%   $128.2823   $128.28   $128.30   $128.30  
  Purchase #5 $156.57   6.569%   $166.8551   $166.86   $166.85   $166.90  
  Purchase #6 $183.80   11.409%   $204.7697   $204.77   $204.75   $204.80  
  Purchase #7 $57.38   8.167%   $62.0662   $62.07   $62.05   $62.10  
  7 purchase totals = $937.60       $1,023.0796   $1,023.08   $1,023.10   $1,023.20