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 $65.33   5.238%   $68.752   $68.75   $68.75   $68.80  
  Purchase #2 $230.29   5.651%   $243.3037   $243.30   $243.30   $243.30  
  Purchase #3 $120.64   5.845%   $127.6914   $127.69   $127.70   $127.70  
  Purchase #4 $58.72   8.815%   $63.8962   $63.90   $63.90   $63.90  
  Purchase #5 $73.25   9.744%   $80.3875   $80.39   $80.40   $80.40  
  Purchase #6 $223.84   7.790%   $241.2771   $241.28   $241.30   $241.30  
  Purchase #7 $65.47   5.649%   $69.1684   $69.17   $69.15   $69.20  
  7 purchase totals = $837.54       $894.4763   $894.48   $894.50   $894.60