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 $85.83   7.152%   $91.9686   $91.97   $91.95   $92.00  
  Purchase #2 $74.27   9.351%   $81.215   $81.22   $81.20   $81.20  
  Purchase #3 $228.41   8.832%   $248.5832   $248.58   $248.60   $248.60  
  Purchase #4 $245.73   12.452%   $276.3283   $276.33   $276.35   $276.30  
  Purchase #5 $205.75   9.734%   $225.7777   $225.78   $225.80   $225.80  
  Purchase #6 $159.62   9.686%   $175.0808   $175.08   $175.10   $175.10  
  Purchase #7 $160.33   5.834%   $169.6837   $169.68   $169.70   $169.70  
  7 purchase totals = $1,159.94       $1,268.6373   $1,268.64   $1,268.70   $1,268.70