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 $195.53   7.371%   $209.9425   $209.94   $209.95   $209.90  
  Purchase #2 $39.31   11.712%   $43.914   $43.91   $43.90   $43.90  
  Purchase #3 $126.51   9.721%   $138.808   $138.81   $138.80   $138.80  
  Purchase #4 $148.70   9.779%   $163.2414   $163.24   $163.25   $163.20  
  Purchase #5 $152.49   11.756%   $170.4167   $170.42   $170.40   $170.40  
  Purchase #6 $116.74   10.200%   $128.6475   $128.65   $128.65   $128.60  
  Purchase #7 $58.30   9.771%   $63.9965   $64.00   $64.00   $64.00  
  7 purchase totals = $837.58       $918.9666   $918.97   $918.95   $918.80