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 $88.48   3.447%   $91.5299   $91.53   $91.55   $91.50  
  Purchase #2 $210.50   12.491%   $236.7936   $236.79   $236.80   $236.80  
  Purchase #3 $194.54   3.816%   $201.9636   $201.96   $201.95   $202.00  
  Purchase #4 $42.96   5.242%   $45.212   $45.21   $45.20   $45.20  
  Purchase #5 $238.43   10.645%   $263.8109   $263.81   $263.80   $263.80  
  Purchase #6 $157.62   4.797%   $165.181   $165.18   $165.20   $165.20  
  Purchase #7 $174.30   4.277%   $181.7548   $181.75   $181.75   $181.80  
  7 purchase totals = $1,106.83       $1,186.2458   $1,186.23   $1,186.25   $1,186.30