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 $129.84   11.692%   $145.0209   $145.02   $145.00   $145.00  
  Purchase #2 $105.39   3.735%   $109.3263   $109.33   $109.35   $109.30  
  Purchase #3 $246.44   3.546%   $255.1788   $255.18   $255.20   $255.20  
  Purchase #4 $125.65   6.418%   $133.7142   $133.71   $133.70   $133.70  
  Purchase #5 $214.86   4.138%   $223.7509   $223.75   $223.75   $223.80  
  Purchase #6 $187.73   7.470%   $201.7534   $201.75   $201.75   $201.80  
  Purchase #7 $24.36   6.764%   $26.0077   $26.01   $26.00   $26.00  
  7 purchase totals = $1,034.27       $1,094.7522   $1,094.75   $1,094.75   $1,094.80