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 $68.84   5.755%   $72.8017   $72.80   $72.80   $72.80  
  Purchase #2 $33.75   9.424%   $36.9306   $36.93   $36.95   $36.90  
  Purchase #3 $151.37   8.173%   $163.7415   $163.74   $163.75   $163.70  
  Purchase #4 $24.72   13.102%   $27.9588   $27.96   $27.95   $28.00  
  Purchase #5 $167.74   13.364%   $190.1568   $190.16   $190.15   $190.20  
  Purchase #6 $185.79   5.770%   $196.5101   $196.51   $196.50   $196.50  
  Purchase #7 $131.28   11.107%   $145.8613   $145.86   $145.85   $145.90  
  7 purchase totals = $763.49       $833.9608   $833.96   $833.95   $834.00