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 $174.49   11.347%   $194.2894   $194.29   $194.30   $194.30  
  Purchase #2 $228.96   7.750%   $246.7044   $246.70   $246.70   $246.70  
  Purchase #3 $23.27   6.117%   $24.6934   $24.69   $24.70   $24.70  
  Purchase #4 $98.35   9.416%   $107.6106   $107.61   $107.60   $107.60  
  Purchase #5 $23.97   5.806%   $25.3617   $25.36   $25.35   $25.40  
  Purchase #6 $187.75   12.507%   $211.2319   $211.23   $211.25   $211.20  
  Purchase #7 $28.90   7.319%   $31.0152   $31.02   $31.00   $31.00  
  7 purchase totals = $765.69       $840.9066   $840.90   $840.90   $840.90