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 $91.77   3.227%   $94.7314   $94.73   $94.75   $94.70  
  Purchase #2 $95.80   8.242%   $103.6958   $103.70   $103.70   $103.70  
  Purchase #3 $80.43   3.220%   $83.0198   $83.02   $83.00   $83.00  
  Purchase #4 $105.94   3.391%   $109.5324   $109.53   $109.55   $109.50  
  Purchase #5 $102.93   7.835%   $110.9946   $110.99   $111.00   $111.00  
  Purchase #6 $145.95   12.761%   $164.5747   $164.57   $164.55   $164.60  
  Purchase #7 $100.69   6.474%   $107.2087   $107.21   $107.20   $107.20  
  7 purchase totals = $723.51       $773.7574   $773.75   $773.75   $773.70