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 $233.61   6.260%   $248.234   $248.23   $248.25   $248.20  
  Purchase #2 $235.57   10.627%   $260.604   $260.60   $260.60   $260.60  
  Purchase #3 $34.38   13.775%   $39.1158   $39.12   $39.10   $39.10  
  Purchase #4 $36.27   11.761%   $40.5357   $40.54   $40.55   $40.50  
  Purchase #5 $190.66   6.456%   $202.969   $202.97   $202.95   $203.00  
  Purchase #6 $121.90   6.707%   $130.0758   $130.08   $130.10   $130.10  
  Purchase #7 $89.79   9.535%   $98.3515   $98.35   $98.35   $98.40  
  7 purchase totals = $942.18       $1,019.8858   $1,019.89   $1,019.90   $1,019.90