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 $89.46   5.333%   $94.2309   $94.23   $94.25   $94.20  
  Purchase #2 $16.57   9.269%   $18.1059   $18.11   $18.10   $18.10  
  Purchase #3 $244.96   11.473%   $273.0643   $273.06   $273.05   $273.10  
  Purchase #4 $142.48   5.184%   $149.8662   $149.87   $149.85   $149.90  
  Purchase #5 $69.99   10.753%   $77.516   $77.52   $77.50   $77.50  
  Purchase #6 $209.96   6.364%   $223.3219   $223.32   $223.30   $223.30  
  Purchase #7 $211.39   5.502%   $223.0207   $223.02   $223.00   $223.00  
  7 purchase totals = $984.81       $1,059.1259   $1,059.13   $1,059.05   $1,059.10