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 $205.72   10.194%   $226.6911   $226.69   $226.70   $226.70  
  Purchase #2 $168.32   3.374%   $173.9991   $174.00   $174.00   $174.00  
  Purchase #3 $95.35   11.405%   $106.2247   $106.22   $106.20   $106.20  
  Purchase #4 $159.67   11.141%   $177.4588   $177.46   $177.45   $177.50  
  Purchase #5 $139.58   12.107%   $156.479   $156.48   $156.50   $156.50  
  Purchase #6 $38.29   10.387%   $42.2672   $42.27   $42.25   $42.30  
  Purchase #7 $138.88   7.644%   $149.496   $149.50   $149.50   $149.50  
  7 purchase totals = $945.81       $1,032.6159   $1,032.62   $1,032.60   $1,032.70