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 $172.35   3.634%   $178.6132   $178.61   $178.60   $178.60  
  Purchase #2 $138.26   6.306%   $146.9787   $146.98   $147.00   $147.00  
  Purchase #3 $249.47   5.500%   $263.1909   $263.19   $263.20   $263.20  
  Purchase #4 $17.33   11.454%   $19.315   $19.32   $19.30   $19.30  
  Purchase #5 $178.76   11.169%   $198.7257   $198.73   $198.75   $198.70  
  Purchase #6 $38.82   6.566%   $41.3689   $41.37   $41.35   $41.40  
  Purchase #7 $29.28   12.218%   $32.8574   $32.86   $32.85   $32.90  
  7 purchase totals = $824.27       $881.0498   $881.06   $881.05   $881.10