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 $172.51   3.175%   $177.9872   $177.99   $178.00   $178.00  
  Purchase #2 $152.31   5.405%   $160.5424   $160.54   $160.55   $160.50  
  Purchase #3 $9.62   5.566%   $10.1554   $10.16   $10.15   $10.20  
  Purchase #4 $177.26   9.608%   $194.2911   $194.29   $194.30   $194.30  
  Purchase #5 $243.51   5.814%   $257.6677   $257.67   $257.65   $257.70  
  Purchase #6 $175.55   12.220%   $197.0022   $197.00   $197.00   $197.00  
  Purchase #7 $216.97   11.701%   $242.3577   $242.36   $242.35   $242.40  
  7 purchase totals = $1,147.73       $1,240.0037   $1,240.01   $1,240.00   $1,240.10