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 $5.58   5.370%   $5.8796   $5.88   $5.90   $5.90  
  Purchase #2 $71.96   5.179%   $75.6868   $75.69   $75.70   $75.70  
  Purchase #3 $132.42   4.699%   $138.6424   $138.64   $138.65   $138.60  
  Purchase #4 $23.45   10.700%   $25.9592   $25.96   $25.95   $26.00  
  Purchase #5 $14.51   13.225%   $16.4289   $16.43   $16.45   $16.40  
  Purchase #6 $94.77   13.659%   $107.7146   $107.71   $107.70   $107.70  
  Purchase #7 $34.79   9.215%   $37.9959   $38.00   $38.00   $38.00  
  7 purchase totals = $377.48       $408.3074   $408.31   $408.35   $408.30