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 $204.91   8.194%   $221.7003   $221.70   $221.70   $221.70  
  Purchase #2 $23.32   12.333%   $26.1961   $26.20   $26.20   $26.20  
  Purchase #3 $232.36   13.836%   $264.5093   $264.51   $264.50   $264.50  
  Purchase #4 $127.79   6.172%   $135.6772   $135.68   $135.70   $135.70  
  Purchase #5 $5.93   3.185%   $6.1189   $6.12   $6.10   $6.10  
  Purchase #6 $237.28   13.845%   $270.1314   $270.13   $270.15   $270.10  
  Purchase #7 $49.68   10.423%   $54.8581   $54.86   $54.85   $54.90  
  7 purchase totals = $881.27       $979.1913   $979.20   $979.20   $979.20