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 $246.34   3.562%   $255.1146   $255.11   $255.10   $255.10  
  Purchase #2 $27.94   4.835%   $29.2909   $29.29   $29.30   $29.30  
  Purchase #3 $154.26   3.831%   $160.1697   $160.17   $160.15   $160.20  
  Purchase #4 $8.87   7.374%   $9.5241   $9.52   $9.50   $9.50  
  Purchase #5 $241.53   10.770%   $267.5428   $267.54   $267.55   $267.50  
  Purchase #6 $226.91   10.675%   $251.1326   $251.13   $251.15   $251.10  
  Purchase #7 $218.73   4.362%   $228.271   $228.27   $228.25   $228.30  
  7 purchase totals = $1,124.58       $1,201.0457   $1,201.03   $1,201.00   $1,201.00