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 $54.42   10.136%   $59.936   $59.94   $59.95   $59.90  
  Purchase #2 $197.49   9.771%   $216.7867   $216.79   $216.80   $216.80  
  Purchase #3 $200.32   6.107%   $212.5535   $212.55   $212.55   $212.60  
  Purchase #4 $151.94   9.371%   $166.1783   $166.18   $166.20   $166.20  
  Purchase #5 $107.98   13.248%   $122.2852   $122.29   $122.30   $122.30  
  Purchase #6 $92.39   6.641%   $98.5256   $98.53   $98.55   $98.50  
  Purchase #7 $103.31   3.218%   $106.6345   $106.63   $106.65   $106.60  
  7 purchase totals = $907.85       $982.8998   $982.91   $983.00   $982.90