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 $67.44   5.717%   $71.2955   $71.30   $71.30   $71.30  
  Purchase #2 $32.95   4.788%   $34.5276   $34.53   $34.55   $34.50  
  Purchase #3 $169.95   12.711%   $191.5523   $191.55   $191.55   $191.60  
  Purchase #4 $210.65   4.415%   $219.9502   $219.95   $219.95   $220.00  
  Purchase #5 $192.65   6.214%   $204.6213   $204.62   $204.60   $204.60  
  Purchase #6 $125.71   8.232%   $136.0584   $136.06   $136.05   $136.10  
  Purchase #7 $184.37   4.545%   $192.7496   $192.75   $192.75   $192.70  
  7 purchase totals = $983.72       $1,050.7549   $1,050.76   $1,050.75   $1,050.80