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 $62.38   9.630%   $68.3872   $68.39   $68.40   $68.40  
  Purchase #2 $81.68   5.267%   $85.9821   $85.98   $86.00   $86.00  
  Purchase #3 $147.85   7.758%   $159.3202   $159.32   $159.30   $159.30  
  Purchase #4 $153.52   13.198%   $173.7816   $173.78   $173.80   $173.80  
  Purchase #5 $52.41   4.585%   $54.813   $54.81   $54.80   $54.80  
  Purchase #6 $167.43   6.700%   $178.6478   $178.65   $178.65   $178.60  
  Purchase #7 $40.62   9.809%   $44.6044   $44.60   $44.60   $44.60  
  7 purchase totals = $705.89       $765.5363   $765.53   $765.55   $765.50