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 $88.96   12.563%   $100.136   $100.14   $100.15   $100.10  
  Purchase #2 $65.86   9.247%   $71.9501   $71.95   $71.95   $72.00  
  Purchase #3 $80.96   8.633%   $87.9493   $87.95   $87.95   $87.90  
  Purchase #4 $135.97   8.474%   $147.4921   $147.49   $147.50   $147.50  
  Purchase #5 $224.37   6.474%   $238.8957   $238.90   $238.90   $238.90  
  Purchase #6 $75.79   10.166%   $83.4948   $83.49   $83.50   $83.50  
  Purchase #7 $203.98   9.787%   $223.9435   $223.94   $223.95   $223.90  
  7 purchase totals = $875.89       $953.8615   $953.86   $953.90   $953.80