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 $172.70   4.675%   $180.7737   $180.77   $180.75   $180.80  
  Purchase #2 $142.73   3.459%   $147.667   $147.67   $147.65   $147.70  
  Purchase #3 $40.42   7.831%   $43.5853   $43.59   $43.60   $43.60  
  Purchase #4 $29.71   6.276%   $31.5746   $31.57   $31.55   $31.60  
  Purchase #5 $92.76   12.166%   $104.0452   $104.05   $104.05   $104.00  
  Purchase #6 $31.26   5.555%   $32.9965   $33.00   $33.00   $33.00  
  Purchase #7 $65.95   8.793%   $71.749   $71.75   $71.75   $71.70  
  7 purchase totals = $575.53       $612.3913   $612.40   $612.35   $612.40