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 $44.88   11.322%   $49.9613   $49.96   $49.95   $50.00  
  Purchase #2 $23.72   4.148%   $24.7039   $24.70   $24.70   $24.70  
  Purchase #3 $140.98   11.333%   $156.9573   $156.96   $156.95   $157.00  
  Purchase #4 $182.95   11.392%   $203.7917   $203.79   $203.80   $203.80  
  Purchase #5 $189.82   5.239%   $199.7647   $199.76   $199.75   $199.80  
  Purchase #6 $169.58   5.384%   $178.7102   $178.71   $178.70   $178.70  
  Purchase #7 $155.65   4.280%   $162.3118   $162.31   $162.30   $162.30  
  7 purchase totals = $907.58       $976.2009   $976.19   $976.15   $976.30