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 $85.70   11.190%   $95.2898   $95.29   $95.30   $95.30  
  Purchase #2 $159.67   9.238%   $174.4203   $174.42   $174.40   $174.40  
  Purchase #3 $70.47   11.411%   $78.5113   $78.51   $78.50   $78.50  
  Purchase #4 $236.92   3.176%   $244.4446   $244.44   $244.45   $244.40  
  Purchase #5 $188.86   11.703%   $210.9623   $210.96   $210.95   $211.00  
  Purchase #6 $248.68   8.737%   $270.4072   $270.41   $270.40   $270.40  
  Purchase #7 $202.84   11.457%   $226.0794   $226.08   $226.10   $226.10  
  7 purchase totals = $1,193.14       $1,300.1149   $1,300.11   $1,300.10   $1,300.10