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 $59.72   8.282%   $64.666   $64.67   $64.65   $64.70  
  Purchase #2 $138.40   3.282%   $142.9423   $142.94   $142.95   $142.90  
  Purchase #3 $149.40   11.844%   $167.0949   $167.09   $167.10   $167.10  
  Purchase #4 $95.56   12.414%   $107.4228   $107.42   $107.40   $107.40  
  Purchase #5 $13.52   8.149%   $14.6217   $14.62   $14.60   $14.60  
  Purchase #6 $189.84   12.496%   $213.5624   $213.56   $213.55   $213.60  
  Purchase #7 $120.59   3.797%   $125.1688   $125.17   $125.15   $125.20  
  7 purchase totals = $767.03       $835.4789   $835.47   $835.40   $835.50