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 $211.46   6.119%   $224.3992   $224.40   $224.40   $224.40  
  Purchase #2 $167.69   9.506%   $183.6306   $183.63   $183.65   $183.60  
  Purchase #3 $7.45   12.222%   $8.3605   $8.36   $8.35   $8.40  
  Purchase #4 $241.98   7.456%   $260.022   $260.02   $260.00   $260.00  
  Purchase #5 $42.26   4.411%   $44.1241   $44.12   $44.10   $44.10  
  Purchase #6 $123.61   9.608%   $135.4864   $135.49   $135.50   $135.50  
  Purchase #7 $202.70   3.770%   $210.3418   $210.34   $210.35   $210.30  
  7 purchase totals = $997.15       $1,066.3646   $1,066.36   $1,066.35   $1,066.30