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 $88.25   10.746%   $97.7333   $97.73   $97.75   $97.70  
  Purchase #2 $204.74   9.584%   $224.3623   $224.36   $224.35   $224.40  
  Purchase #3 $196.86   6.359%   $209.3783   $209.38   $209.40   $209.40  
  Purchase #4 $182.72   11.608%   $203.9301   $203.93   $203.95   $203.90  
  Purchase #5 $10.32   8.802%   $11.2284   $11.23   $11.25   $11.20  
  Purchase #6 $180.37   7.573%   $194.0294   $194.03   $194.05   $194.00  
  Purchase #7 $102.79   6.825%   $109.8054   $109.81   $109.80   $109.80  
  7 purchase totals = $966.05       $1,050.4672   $1,050.47   $1,050.55   $1,050.40