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 $60.56   9.126%   $66.0867   $66.09   $66.10   $66.10  
  Purchase #2 $216.99   9.278%   $237.1223   $237.12   $237.10   $237.10  
  Purchase #3 $102.86   5.656%   $108.6778   $108.68   $108.70   $108.70  
  Purchase #4 $244.42   10.391%   $269.8177   $269.82   $269.80   $269.80  
  Purchase #5 $116.50   12.250%   $130.7713   $130.77   $130.75   $130.80  
  Purchase #6 $150.51   7.332%   $161.5454   $161.55   $161.55   $161.50  
  Purchase #7 $122.66   13.187%   $138.8352   $138.84   $138.85   $138.80  
  7 purchase totals = $1,014.50       $1,112.8564   $1,112.87   $1,112.85   $1,112.80