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 $183.62   10.305%   $202.542   $202.54   $202.55   $202.50  
  Purchase #2 $13.25   8.272%   $14.346   $14.35   $14.35   $14.30  
  Purchase #3 $178.68   8.230%   $193.3854   $193.39   $193.40   $193.40  
  Purchase #4 $71.95   3.264%   $74.2984   $74.30   $74.30   $74.30  
  Purchase #5 $117.52   7.506%   $126.3411   $126.34   $126.35   $126.30  
  Purchase #6 $120.52   5.764%   $127.4668   $127.47   $127.45   $127.50  
  Purchase #7 $52.92   8.777%   $57.5648   $57.56   $57.55   $57.60  
  7 purchase totals = $738.46       $795.9445   $795.95   $795.95   $795.90