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 $197.94   11.744%   $221.1861   $221.19   $221.20   $221.20  
  Purchase #2 $141.45   4.414%   $147.6936   $147.69   $147.70   $147.70  
  Purchase #3 $244.55   4.450%   $255.4325   $255.43   $255.45   $255.40  
  Purchase #4 $219.53   5.806%   $232.2759   $232.28   $232.30   $232.30  
  Purchase #5 $60.60   8.771%   $65.9152   $65.92   $65.90   $65.90  
  Purchase #6 $61.97   5.390%   $65.3102   $65.31   $65.30   $65.30  
  Purchase #7 $248.57   10.143%   $273.7825   $273.78   $273.80   $273.80  
  7 purchase totals = $1,174.61       $1,261.5960   $1,261.60   $1,261.65   $1,261.60