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 $182.67   11.166%   $203.0669   $203.07   $203.05   $203.10  
  Purchase #2 $56.57   10.514%   $62.5178   $62.52   $62.50   $62.50  
  Purchase #3 $140.87   11.178%   $156.6164   $156.62   $156.60   $156.60  
  Purchase #4 $174.98   4.786%   $183.3545   $183.35   $183.35   $183.40  
  Purchase #5 $91.81   9.562%   $100.5889   $100.59   $100.60   $100.60  
  Purchase #6 $129.34   7.222%   $138.6809   $138.68   $138.70   $138.70  
  Purchase #7 $98.99   10.638%   $109.5206   $109.52   $109.50   $109.50  
  7 purchase totals = $875.23       $954.3460   $954.35   $954.30   $954.40