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 $31.96   12.339%   $35.9035   $35.90   $35.90   $35.90  
  Purchase #2 $184.97   10.265%   $203.9572   $203.96   $203.95   $204.00  
  Purchase #3 $75.25   13.489%   $85.4005   $85.40   $85.40   $85.40  
  Purchase #4 $115.71   7.672%   $124.5873   $124.59   $124.60   $124.60  
  Purchase #5 $57.25   13.501%   $64.9793   $64.98   $65.00   $65.00  
  Purchase #6 $215.98   4.473%   $225.6408   $225.64   $225.65   $225.60  
  Purchase #7 $111.44   7.165%   $119.4247   $119.42   $119.40   $119.40  
  7 purchase totals = $792.56       $859.8933   $859.89   $859.90   $859.90