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 $34.68   8.306%   $37.5605   $37.56   $37.55   $37.60  
  Purchase #2 $229.77   6.293%   $244.2294   $244.23   $244.25   $244.20  
  Purchase #3 $202.42   4.335%   $211.1949   $211.19   $211.20   $211.20  
  Purchase #4 $40.25   11.560%   $44.9029   $44.90   $44.90   $44.90  
  Purchase #5 $183.66   11.305%   $204.4228   $204.42   $204.40   $204.40  
  Purchase #6 $134.57   11.280%   $149.7495   $149.75   $149.75   $149.70  
  Purchase #7 $108.28   6.421%   $115.2327   $115.23   $115.25   $115.20  
  7 purchase totals = $933.63       $1,007.2927   $1,007.28   $1,007.30   $1,007.20