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 $183.26   8.764%   $199.3209   $199.32   $199.30   $199.30  
  Purchase #2 $201.50   9.121%   $219.8788   $219.88   $219.90   $219.90  
  Purchase #3 $44.91   11.689%   $50.1595   $50.16   $50.15   $50.20  
  Purchase #4 $105.75   11.745%   $118.1703   $118.17   $118.15   $118.20  
  Purchase #5 $217.78   12.220%   $244.3927   $244.39   $244.40   $244.40  
  Purchase #6 $108.31   12.242%   $121.5693   $121.57   $121.55   $121.60  
  Purchase #7 $87.36   6.111%   $92.6986   $92.70   $92.70   $92.70  
  7 purchase totals = $948.87       $1,046.1901   $1,046.19   $1,046.15   $1,046.30