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 $241.86   5.156%   $254.3303   $254.33   $254.35   $254.30  
  Purchase #2 $53.99   11.584%   $60.2442   $60.24   $60.25   $60.20  
  Purchase #3 $19.63   3.566%   $20.33   $20.33   $20.35   $20.30  
  Purchase #4 $87.46   5.702%   $92.447   $92.45   $92.45   $92.40  
  Purchase #5 $60.44   13.868%   $68.8218   $68.82   $68.80   $68.80  
  Purchase #6 $181.25   6.869%   $193.7001   $193.70   $193.70   $193.70  
  Purchase #7 $54.65   5.362%   $57.5803   $57.58   $57.60   $57.60  
  7 purchase totals = $699.28       $747.4537   $747.45   $747.50   $747.30