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 $118.58   13.256%   $134.299   $134.30   $134.30   $134.30  
  Purchase #2 $55.42   11.813%   $61.9668   $61.97   $61.95   $62.00  
  Purchase #3 $168.67   7.405%   $181.16   $181.16   $181.15   $181.20  
  Purchase #4 $118.45   13.423%   $134.3495   $134.35   $134.35   $134.30  
  Purchase #5 $91.75   9.525%   $100.4892   $100.49   $100.50   $100.50  
  Purchase #6 $161.84   11.194%   $179.9564   $179.96   $179.95   $180.00  
  Purchase #7 $39.29   12.460%   $44.1855   $44.19   $44.20   $44.20  
  7 purchase totals = $754.00       $836.4064   $836.42   $836.40   $836.50