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 $175.33   12.382%   $197.0394   $197.04   $197.05   $197.00  
  Purchase #2 $71.26   7.250%   $76.4264   $76.43   $76.45   $76.40  
  Purchase #3 $233.86   10.764%   $259.0327   $259.03   $259.05   $259.00  
  Purchase #4 $139.65   3.280%   $144.2305   $144.23   $144.25   $144.20  
  Purchase #5 $141.39   10.594%   $156.3689   $156.37   $156.35   $156.40  
  Purchase #6 $201.35   11.237%   $223.9757   $223.98   $224.00   $224.00  
  Purchase #7 $34.34   7.741%   $36.9983   $37.00   $37.00   $37.00  
  7 purchase totals = $997.18       $1,094.0719   $1,094.08   $1,094.15   $1,094.00