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 $114.35   3.690%   $118.5695   $118.57   $118.55   $118.60  
  Purchase #2 $225.79   4.335%   $235.578   $235.58   $235.60   $235.60  
  Purchase #3 $33.52   10.560%   $37.0597   $37.06   $37.05   $37.10  
  Purchase #4 $61.30   8.535%   $66.532   $66.53   $66.55   $66.50  
  Purchase #5 $154.49   12.420%   $173.6777   $173.68   $173.70   $173.70  
  Purchase #6 $70.89   6.639%   $75.5964   $75.60   $75.60   $75.60  
  Purchase #7 $147.82   12.529%   $166.3404   $166.34   $166.35   $166.30  
  7 purchase totals = $808.16       $873.3537   $873.36   $873.40   $873.40