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 $181.80   12.552%   $204.6195   $204.62   $204.60   $204.60  
  Purchase #2 $198.64   10.171%   $218.8437   $218.84   $218.85   $218.80  
  Purchase #3 $89.34   13.692%   $101.5724   $101.57   $101.55   $101.60  
  Purchase #4 $174.35   10.717%   $193.0351   $193.04   $193.05   $193.00  
  Purchase #5 $48.81   11.182%   $54.2679   $54.27   $54.25   $54.30  
  Purchase #6 $174.67   10.232%   $192.5422   $192.54   $192.55   $192.50  
  Purchase #7 $83.93   13.558%   $95.3092   $95.31   $95.30   $95.30  
  7 purchase totals = $951.54       $1,060.1900   $1,060.19   $1,060.15   $1,060.10