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 $181.85   12.566%   $204.7013   $204.70   $204.70   $204.70  
  Purchase #2 $94.43   3.318%   $97.5632   $97.56   $97.55   $97.60  
  Purchase #3 $71.52   9.170%   $78.0784   $78.08   $78.10   $78.10  
  Purchase #4 $177.56   12.311%   $199.4194   $199.42   $199.40   $199.40  
  Purchase #5 $136.25   11.103%   $151.3778   $151.38   $151.40   $151.40  
  Purchase #6 $209.96   11.599%   $234.3133   $234.31   $234.30   $234.30  
  Purchase #7 $108.98   4.502%   $113.8863   $113.89   $113.90   $113.90  
  7 purchase totals = $980.55       $1,079.3397   $1,079.34   $1,079.35   $1,079.40