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 $115.75   8.696%   $125.8156   $125.82   $125.80   $125.80  
  Purchase #2 $244.34   3.694%   $253.3659   $253.37   $253.35   $253.40  
  Purchase #3 $162.46   7.528%   $174.69   $174.69   $174.70   $174.70  
  Purchase #4 $80.52   5.621%   $85.046   $85.05   $85.05   $85.00  
  Purchase #5 $168.79   4.764%   $176.8312   $176.83   $176.85   $176.80  
  Purchase #6 $135.62   10.484%   $149.8384   $149.84   $149.85   $149.80  
  Purchase #7 $77.29   13.603%   $87.8038   $87.80   $87.80   $87.80  
  7 purchase totals = $984.77       $1,053.3909   $1,053.40   $1,053.40   $1,053.30