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 $191.38   9.218%   $209.0214   $209.02   $209.00   $209.00  
  Purchase #2 $202.43   3.407%   $209.3268   $209.33   $209.35   $209.30  
  Purchase #3 $106.96   11.767%   $119.546   $119.55   $119.55   $119.50  
  Purchase #4 $22.47   13.824%   $25.5763   $25.58   $25.60   $25.60  
  Purchase #5 $222.94   8.327%   $241.5042   $241.50   $241.50   $241.50  
  Purchase #6 $171.87   10.453%   $189.8356   $189.84   $189.85   $189.80  
  Purchase #7 $46.31   12.552%   $52.1228   $52.12   $52.10   $52.10  
  7 purchase totals = $964.36       $1,046.9331   $1,046.94   $1,046.95   $1,046.80