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 $180.94   9.184%   $197.5575   $197.56   $197.55   $197.60  
  Purchase #2 $239.48   7.632%   $257.7571   $257.76   $257.75   $257.80  
  Purchase #3 $237.98   11.306%   $264.886   $264.89   $264.90   $264.90  
  Purchase #4 $126.93   13.831%   $144.4857   $144.49   $144.50   $144.50  
  Purchase #5 $54.77   9.126%   $59.7683   $59.77   $59.75   $59.80  
  Purchase #6 $214.42   6.698%   $228.7819   $228.78   $228.80   $228.80  
  Purchase #7 $37.52   9.185%   $40.9662   $40.97   $40.95   $41.00  
  7 purchase totals = $1,092.04       $1,194.2027   $1,194.22   $1,194.20   $1,194.40