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 $136.75   12.656%   $154.0571   $154.06   $154.05   $154.10  
  Purchase #2 $51.66   5.414%   $54.4569   $54.46   $54.45   $54.50  
  Purchase #3 $240.56   4.439%   $251.2385   $251.24   $251.25   $251.20  
  Purchase #4 $237.52   7.816%   $256.0846   $256.08   $256.10   $256.10  
  Purchase #5 $18.85   11.108%   $20.9439   $20.94   $20.95   $20.90  
  Purchase #6 $44.96   11.123%   $49.9609   $49.96   $49.95   $50.00  
  Purchase #7 $158.30   3.111%   $163.2247   $163.22   $163.20   $163.20  
  7 purchase totals = $888.60       $949.9666   $949.96   $949.95   $950.00