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 $174.65   3.281%   $180.3803   $180.38   $180.40   $180.40  
  Purchase #2 $10.35   10.299%   $11.4159   $11.42   $11.40   $11.40  
  Purchase #3 $30.55   9.348%   $33.4058   $33.41   $33.40   $33.40  
  Purchase #4 $129.79   12.298%   $145.7516   $145.75   $145.75   $145.80  
  Purchase #5 $87.28   8.707%   $94.8795   $94.88   $94.90   $94.90  
  Purchase #6 $14.37   6.700%   $15.3328   $15.33   $15.35   $15.30  
  Purchase #7 $113.81   3.250%   $117.5088   $117.51   $117.50   $117.50  
  7 purchase totals = $560.80       $598.6747   $598.68   $598.70   $598.70