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 $175.44   11.161%   $195.0209   $195.02   $195.00   $195.00  
  Purchase #2 $212.27   12.148%   $238.0566   $238.06   $238.05   $238.10  
  Purchase #3 $246.65   10.861%   $273.4387   $273.44   $273.45   $273.40  
  Purchase #4 $196.84   7.447%   $211.4987   $211.50   $211.50   $211.50  
  Purchase #5 $51.81   8.564%   $56.247   $56.25   $56.25   $56.20  
  Purchase #6 $180.73   7.332%   $193.9811   $193.98   $194.00   $194.00  
  Purchase #7 $150.74   6.585%   $160.6662   $160.67   $160.65   $160.70  
  7 purchase totals = $1,214.48       $1,328.9092   $1,328.92   $1,328.90   $1,328.90