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 $82.74   10.814%   $91.6875   $91.69   $91.70   $91.70  
  Purchase #2 $160.55   11.273%   $178.6488   $178.65   $178.65   $178.60  
  Purchase #3 $183.56   6.322%   $195.1647   $195.16   $195.15   $195.20  
  Purchase #4 $126.74   5.138%   $133.2519   $133.25   $133.25   $133.30  
  Purchase #5 $141.44   7.147%   $151.5487   $151.55   $151.55   $151.50  
  Purchase #6 $127.69   8.536%   $138.5896   $138.59   $138.60   $138.60  
  Purchase #7 $108.52   4.408%   $113.3036   $113.30   $113.30   $113.30  
  7 purchase totals = $931.24       $1,002.1948   $1,002.19   $1,002.20   $1,002.20