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 $175.66   10.210%   $193.5949   $193.59   $193.60   $193.60  
  Purchase #2 $149.41   9.331%   $163.3514   $163.35   $163.35   $163.40  
  Purchase #3 $46.58   6.637%   $49.6715   $49.67   $49.65   $49.70  
  Purchase #4 $60.53   11.800%   $67.6725   $67.67   $67.65   $67.70  
  Purchase #5 $132.74   5.350%   $139.8416   $139.84   $139.85   $139.80  
  Purchase #6 $222.33   11.477%   $247.8468   $247.85   $247.85   $247.80  
  Purchase #7 $168.51   13.334%   $190.9791   $190.98   $191.00   $191.00  
  7 purchase totals = $955.76       $1,052.9578   $1,052.95   $1,052.95   $1,053.00