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 $26.40   7.486%   $28.3763   $28.38   $28.40   $28.40  
  Purchase #2 $158.38   9.158%   $172.8844   $172.88   $172.90   $172.90  
  Purchase #3 $203.33   10.437%   $224.5516   $224.55   $224.55   $224.60  
  Purchase #4 $169.73   13.191%   $192.1191   $192.12   $192.10   $192.10  
  Purchase #5 $20.93   8.219%   $22.6502   $22.65   $22.65   $22.70  
  Purchase #6 $131.57   10.347%   $145.1835   $145.18   $145.20   $145.20  
  Purchase #7 $97.36   7.842%   $104.995   $105.00   $105.00   $105.00  
  7 purchase totals = $807.70       $890.7601   $890.76   $890.80   $890.90