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 $98.68   7.504%   $106.0849   $106.08   $106.10   $106.10  
  Purchase #2 $90.31   6.143%   $95.8577   $95.86   $95.85   $95.90  
  Purchase #3 $90.76   5.432%   $95.6901   $95.69   $95.70   $95.70  
  Purchase #4 $21.94   4.614%   $22.9523   $22.95   $22.95   $23.00  
  Purchase #5 $189.73   11.769%   $212.0593   $212.06   $212.05   $212.10  
  Purchase #6 $245.73   9.809%   $269.8337   $269.83   $269.85   $269.80  
  Purchase #7 $248.96   3.567%   $257.8404   $257.84   $257.85   $257.80  
  7 purchase totals = $986.11       $1,060.3184   $1,060.31   $1,060.35   $1,060.40