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 $190.65   12.226%   $213.9589   $213.96   $213.95   $214.00  
  Purchase #2 $50.28   7.397%   $53.9992   $54.00   $54.00   $54.00  
  Purchase #3 $57.47   10.794%   $63.6733   $63.67   $63.65   $63.70  
  Purchase #4 $230.32   11.811%   $257.5231   $257.52   $257.50   $257.50  
  Purchase #5 $130.81   10.125%   $144.0545   $144.05   $144.05   $144.10  
  Purchase #6 $113.39   13.391%   $128.5741   $128.57   $128.55   $128.60  
  Purchase #7 $177.58   3.680%   $184.1149   $184.11   $184.10   $184.10  
  7 purchase totals = $950.50       $1,045.8980   $1,045.88   $1,045.80   $1,046.00