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 $190.93   6.328%   $203.0121   $203.01   $203.00   $203.00  
  Purchase #2 $100.97   5.693%   $106.7182   $106.72   $106.70   $106.70  
  Purchase #3 $128.27   7.584%   $137.998   $138.00   $138.00   $138.00  
  Purchase #4 $44.34   9.575%   $48.5856   $48.59   $48.60   $48.60  
  Purchase #5 $218.78   9.692%   $239.9842   $239.98   $240.00   $240.00  
  Purchase #6 $176.81   11.760%   $197.6029   $197.60   $197.60   $197.60  
  Purchase #7 $115.58   9.552%   $126.6202   $126.62   $126.60   $126.60  
  7 purchase totals = $975.68       $1,060.5212   $1,060.52   $1,060.50   $1,060.50