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 $152.78   13.861%   $173.9568   $173.96   $173.95   $174.00  
  Purchase #2 $115.95   11.854%   $129.6947   $129.69   $129.70   $129.70  
  Purchase #3 $85.79   10.162%   $94.508   $94.51   $94.50   $94.50  
  Purchase #4 $49.72   8.637%   $54.0143   $54.01   $54.00   $54.00  
  Purchase #5 $177.82   8.580%   $193.077   $193.08   $193.10   $193.10  
  Purchase #6 $183.27   5.478%   $193.3095   $193.31   $193.30   $193.30  
  Purchase #7 $126.91   3.387%   $131.2084   $131.21   $131.20   $131.20  
  7 purchase totals = $892.24       $969.7687   $969.77   $969.75   $969.80