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 $64.94   12.527%   $73.075   $73.08   $73.10   $73.10  
  Purchase #2 $194.80   10.143%   $214.5586   $214.56   $214.55   $214.60  
  Purchase #3 $176.48   9.657%   $193.5227   $193.52   $193.50   $193.50  
  Purchase #4 $121.84   5.839%   $128.9542   $128.95   $128.95   $129.00  
  Purchase #5 $187.74   5.627%   $198.3041   $198.30   $198.30   $198.30  
  Purchase #6 $5.52   12.126%   $6.1894   $6.19   $6.20   $6.20  
  Purchase #7 $131.30   11.166%   $145.961   $145.96   $145.95   $146.00  
  7 purchase totals = $882.62       $960.5650   $960.56   $960.55   $960.70