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 $186.84   8.414%   $202.5607   $202.56   $202.55   $202.60  
  Purchase #2 $219.57   9.300%   $239.99   $239.99   $240.00   $240.00  
  Purchase #3 $78.26   8.516%   $84.9246   $84.92   $84.90   $84.90  
  Purchase #4 $50.94   11.562%   $56.8297   $56.83   $56.85   $56.80  
  Purchase #5 $95.28   5.787%   $100.7939   $100.79   $100.80   $100.80  
  Purchase #6 $226.47   7.362%   $243.1427   $243.14   $243.15   $243.10  
  Purchase #7 $88.25   8.496%   $95.7477   $95.75   $95.75   $95.70  
  7 purchase totals = $945.61       $1,023.9893   $1,023.98   $1,024.00   $1,023.90