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 $108.96   9.148%   $118.9277   $118.93   $118.95   $118.90  
  Purchase #2 $135.66   11.444%   $151.1849   $151.18   $151.20   $151.20  
  Purchase #3 $160.99   7.637%   $173.2848   $173.28   $173.30   $173.30  
  Purchase #4 $163.68   5.624%   $172.8854   $172.89   $172.90   $172.90  
  Purchase #5 $115.71   4.825%   $121.293   $121.29   $121.30   $121.30  
  Purchase #6 $227.61   5.736%   $240.6657   $240.67   $240.65   $240.70  
  Purchase #7 $111.94   12.127%   $125.515   $125.52   $125.50   $125.50  
  7 purchase totals = $1,024.55       $1,103.7565   $1,103.76   $1,103.80   $1,103.80