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 $91.29   4.743%   $95.6199   $95.62   $95.60   $95.60  
  Purchase #2 $36.88   13.818%   $41.9761   $41.98   $42.00   $42.00  
  Purchase #3 $162.42   8.431%   $176.1136   $176.11   $176.10   $176.10  
  Purchase #4 $37.40   9.712%   $41.0323   $41.03   $41.05   $41.00  
  Purchase #5 $124.37   3.402%   $128.6011   $128.60   $128.60   $128.60  
  Purchase #6 $140.29   7.625%   $150.9871   $150.99   $151.00   $151.00  
  Purchase #7 $157.93   9.107%   $172.3127   $172.31   $172.30   $172.30  
  7 purchase totals = $750.58       $806.6428   $806.64   $806.65   $806.60