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 $235.87   12.244%   $264.7499   $264.75   $264.75   $264.70  
  Purchase #2 $203.39   4.541%   $212.6259   $212.63   $212.65   $212.60  
  Purchase #3 $193.63   13.349%   $219.4777   $219.48   $219.50   $219.50  
  Purchase #4 $22.97   8.563%   $24.9369   $24.94   $24.95   $24.90  
  Purchase #5 $128.58   11.250%   $143.0453   $143.05   $143.05   $143.00  
  Purchase #6 $244.88   4.334%   $255.4931   $255.49   $255.50   $255.50  
  Purchase #7 $175.94   10.487%   $194.3908   $194.39   $194.40   $194.40  
  7 purchase totals = $1,205.26       $1,314.7196   $1,314.73   $1,314.80   $1,314.60