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 $58.74   12.108%   $65.8522   $65.85   $65.85   $65.90  
  Purchase #2 $151.67   10.598%   $167.744   $167.74   $167.75   $167.70  
  Purchase #3 $90.82   12.302%   $101.9927   $101.99   $102.00   $102.00  
  Purchase #4 $222.46   13.303%   $252.0539   $252.05   $252.05   $252.10  
  Purchase #5 $27.56   6.464%   $29.3415   $29.34   $29.35   $29.30  
  Purchase #6 $185.27   11.590%   $206.7428   $206.74   $206.75   $206.70  
  Purchase #7 $204.44   10.204%   $225.3011   $225.30   $225.30   $225.30  
  7 purchase totals = $940.96       $1,049.0282   $1,049.01   $1,049.05   $1,049.00