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 $241.95   10.493%   $267.3378   $267.34   $267.35   $267.30  
  Purchase #2 $100.43   9.812%   $110.2842   $110.28   $110.30   $110.30  
  Purchase #3 $165.44   11.830%   $185.0116   $185.01   $185.00   $185.00  
  Purchase #4 $180.53   10.381%   $199.2708   $199.27   $199.25   $199.30  
  Purchase #5 $69.94   13.719%   $79.5351   $79.54   $79.55   $79.50  
  Purchase #6 $181.85   11.344%   $202.4791   $202.48   $202.50   $202.50  
  Purchase #7 $145.91   3.242%   $150.6404   $150.64   $150.65   $150.60  
  7 purchase totals = $1,086.05       $1,194.5590   $1,194.56   $1,194.60   $1,194.50