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 $206.50   6.780%   $220.5007   $220.50   $220.50   $220.50  
  Purchase #2 $98.97   3.655%   $102.5874   $102.59   $102.60   $102.60  
  Purchase #3 $197.90   12.869%   $223.3678   $223.37   $223.35   $223.40  
  Purchase #4 $165.70   9.350%   $181.193   $181.19   $181.20   $181.20  
  Purchase #5 $41.68   8.608%   $45.2678   $45.27   $45.25   $45.30  
  Purchase #6 $243.93   6.402%   $259.5464   $259.55   $259.55   $259.50  
  Purchase #7 $104.51   8.393%   $113.2815   $113.28   $113.30   $113.30  
  7 purchase totals = $1,059.19       $1,145.7446   $1,145.75   $1,145.75   $1,145.80