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 $153.26   11.754%   $171.2742   $171.27   $171.25   $171.30  
  Purchase #2 $88.38   7.479%   $94.9899   $94.99   $95.00   $95.00  
  Purchase #3 $141.87   8.220%   $153.5317   $153.53   $153.55   $153.50  
  Purchase #4 $159.43   6.207%   $169.3258   $169.33   $169.35   $169.30  
  Purchase #5 $231.68   11.781%   $258.9742   $258.97   $258.95   $259.00  
  Purchase #6 $115.68   4.315%   $120.6716   $120.67   $120.65   $120.70  
  Purchase #7 $182.39   11.327%   $203.0493   $203.05   $203.05   $203.00  
  7 purchase totals = $1,072.69       $1,171.8167   $1,171.81   $1,171.80   $1,171.80