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 $96.25   10.323%   $106.1859   $106.19   $106.20   $106.20  
  Purchase #2 $114.78   6.802%   $122.5873   $122.59   $122.60   $122.60  
  Purchase #3 $147.35   4.407%   $153.8437   $153.84   $153.85   $153.80  
  Purchase #4 $169.51   9.472%   $185.566   $185.57   $185.55   $185.60  
  Purchase #5 $206.56   3.103%   $212.9696   $212.97   $212.95   $213.00  
  Purchase #6 $34.52   11.188%   $38.3821   $38.38   $38.40   $38.40  
  Purchase #7 $97.40   8.671%   $105.8456   $105.85   $105.85   $105.80  
  7 purchase totals = $866.37       $925.3802   $925.39   $925.40   $925.40