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 $172.31   10.333%   $190.1148   $190.11   $190.10   $190.10  
  Purchase #2 $91.61   12.745%   $103.2857   $103.29   $103.30   $103.30  
  Purchase #3 $127.58   8.454%   $138.3656   $138.37   $138.35   $138.40  
  Purchase #4 $126.36   6.734%   $134.8691   $134.87   $134.85   $134.90  
  Purchase #5 $55.35   5.199%   $58.2276   $58.23   $58.25   $58.20  
  Purchase #6 $42.37   13.599%   $48.1319   $48.13   $48.15   $48.10  
  Purchase #7 $166.69   7.862%   $179.7952   $179.80   $179.80   $179.80  
  7 purchase totals = $782.27       $852.7899   $852.80   $852.80   $852.80