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 $211.84   7.606%   $227.9526   $227.95   $227.95   $228.00  
  Purchase #2 $228.49   9.732%   $250.7266   $250.73   $250.75   $250.70  
  Purchase #3 $29.63   11.313%   $32.982   $32.98   $33.00   $33.00  
  Purchase #4 $120.31   7.486%   $129.3164   $129.32   $129.30   $129.30  
  Purchase #5 $194.54   6.317%   $206.8291   $206.83   $206.85   $206.80  
  Purchase #6 $6.68   6.676%   $7.126   $7.13   $7.15   $7.10  
  Purchase #7 $170.85   7.526%   $183.7082   $183.71   $183.70   $183.70  
  7 purchase totals = $962.34       $1,038.6409   $1,038.65   $1,038.70   $1,038.60