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 $58.84   11.684%   $65.7149   $65.71   $65.70   $65.70  
  Purchase #2 $171.66   6.403%   $182.6514   $182.65   $182.65   $182.70  
  Purchase #3 $203.95   13.359%   $231.1957   $231.20   $231.20   $231.20  
  Purchase #4 $179.70   12.321%   $201.8408   $201.84   $201.85   $201.80  
  Purchase #5 $205.98   6.338%   $219.035   $219.04   $219.05   $219.00  
  Purchase #6 $197.87   3.357%   $204.5125   $204.51   $204.50   $204.50  
  Purchase #7 $36.75   11.250%   $40.8844   $40.88   $40.90   $40.90  
  7 purchase totals = $1,054.75       $1,145.8347   $1,145.83   $1,145.85   $1,145.80