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 $94.69   10.187%   $104.3361   $104.34   $104.35   $104.30  
  Purchase #2 $59.57   11.404%   $66.3634   $66.36   $66.35   $66.40  
  Purchase #3 $122.82   8.454%   $133.2032   $133.20   $133.20   $133.20  
  Purchase #4 $204.65   11.691%   $228.5756   $228.58   $228.60   $228.60  
  Purchase #5 $180.95   9.767%   $198.6234   $198.62   $198.60   $198.60  
  Purchase #6 $104.49   5.653%   $110.3968   $110.40   $110.40   $110.40  
  Purchase #7 $47.61   10.322%   $52.5243   $52.52   $52.50   $52.50  
  7 purchase totals = $814.78       $894.0228   $894.02   $894.00   $894.00