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 $175.51   4.699%   $183.7572   $183.76   $183.75   $183.80  
  Purchase #2 $186.47   9.623%   $204.414   $204.41   $204.40   $204.40  
  Purchase #3 $188.59   4.612%   $197.2878   $197.29   $197.30   $197.30  
  Purchase #4 $68.73   4.677%   $71.9445   $71.94   $71.95   $71.90  
  Purchase #5 $158.78   13.174%   $179.6977   $179.70   $179.70   $179.70  
  Purchase #6 $118.92   12.712%   $134.0371   $134.04   $134.05   $134.00  
  Purchase #7 $203.37   12.483%   $228.7567   $228.76   $228.75   $228.80  
  7 purchase totals = $1,100.37       $1,199.8950   $1,199.90   $1,199.90   $1,199.90