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 $65.38   3.633%   $67.7553   $67.76   $67.75   $67.80  
  Purchase #2 $163.60   6.332%   $173.9592   $173.96   $173.95   $174.00  
  Purchase #3 $243.96   5.733%   $257.9462   $257.95   $257.95   $257.90  
  Purchase #4 $184.41   11.334%   $205.311   $205.31   $205.30   $205.30  
  Purchase #5 $55.42   8.821%   $60.3086   $60.31   $60.30   $60.30  
  Purchase #6 $147.34   13.309%   $166.9495   $166.95   $166.95   $166.90  
  Purchase #7 $178.30   5.305%   $187.7588   $187.76   $187.75   $187.80  
  7 purchase totals = $1,038.41       $1,119.9886   $1,120.00   $1,119.95   $1,120.00