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 $193.60   4.272%   $201.8706   $201.87   $201.85   $201.90  
  Purchase #2 $61.99   11.334%   $69.0159   $69.02   $69.00   $69.00  
  Purchase #3 $213.84   6.702%   $228.1716   $228.17   $228.15   $228.20  
  Purchase #4 $23.94   3.558%   $24.7918   $24.79   $24.80   $24.80  
  Purchase #5 $143.25   5.171%   $150.6575   $150.66   $150.65   $150.70  
  Purchase #6 $112.53   11.534%   $125.5092   $125.51   $125.50   $125.50  
  Purchase #7 $208.37   5.687%   $220.22   $220.22   $220.20   $220.20  
  7 purchase totals = $957.52       $1,020.2366   $1,020.24   $1,020.15   $1,020.30