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 $245.76   8.774%   $267.323   $267.32   $267.30   $267.30  
  Purchase #2 $126.94   4.842%   $133.0864   $133.09   $133.10   $133.10  
  Purchase #3 $71.60   5.803%   $75.7549   $75.75   $75.75   $75.80  
  Purchase #4 $203.27   5.107%   $213.651   $213.65   $213.65   $213.70  
  Purchase #5 $194.68   12.308%   $218.6412   $218.64   $218.65   $218.60  
  Purchase #6 $68.89   9.400%   $75.3657   $75.37   $75.35   $75.40  
  Purchase #7 $50.98   9.778%   $55.9648   $55.96   $55.95   $56.00  
  7 purchase totals = $962.12       $1,039.7870   $1,039.78   $1,039.75   $1,039.90