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 $66.79   5.641%   $70.5576   $70.56   $70.55   $70.60  
  Purchase #2 $197.85   4.426%   $206.6068   $206.61   $206.60   $206.60  
  Purchase #3 $207.73   11.192%   $230.9791   $230.98   $231.00   $231.00  
  Purchase #4 $104.89   5.118%   $110.2583   $110.26   $110.25   $110.30  
  Purchase #5 $167.83   4.507%   $175.3941   $175.39   $175.40   $175.40  
  Purchase #6 $213.69   6.106%   $226.7379   $226.74   $226.75   $226.70  
  Purchase #7 $79.33   10.317%   $87.5145   $87.51   $87.50   $87.50  
  7 purchase totals = $1,038.11       $1,108.0483   $1,108.05   $1,108.05   $1,108.10