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 $146.34   9.480%   $160.213   $160.21   $160.20   $160.20  
  Purchase #2 $69.74   3.667%   $72.2974   $72.30   $72.30   $72.30  
  Purchase #3 $148.52   12.312%   $166.8058   $166.81   $166.80   $166.80  
  Purchase #4 $213.66   8.861%   $232.5924   $232.59   $232.60   $232.60  
  Purchase #5 $165.66   11.621%   $184.9113   $184.91   $184.90   $184.90  
  Purchase #6 $169.46   10.416%   $187.111   $187.11   $187.10   $187.10  
  Purchase #7 $27.84   11.499%   $31.0413   $31.04   $31.05   $31.00  
  7 purchase totals = $941.22       $1,034.9722   $1,034.97   $1,034.95   $1,034.90