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 $206.58   12.485%   $232.3715   $232.37   $232.35   $232.40  
  Purchase #2 $126.52   11.157%   $140.6358   $140.64   $140.65   $140.60  
  Purchase #3 $62.66   3.400%   $64.7904   $64.79   $64.80   $64.80  
  Purchase #4 $85.44   13.169%   $96.6916   $96.69   $96.70   $96.70  
  Purchase #5 $117.76   10.818%   $130.4993   $130.50   $130.50   $130.50  
  Purchase #6 $150.32   11.283%   $167.2806   $167.28   $167.30   $167.30  
  Purchase #7 $34.82   7.166%   $37.3152   $37.32   $37.30   $37.30  
  7 purchase totals = $784.10       $869.5844   $869.59   $869.60   $869.60