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 $134.76   9.529%   $147.6013   $147.60   $147.60   $147.60  
  Purchase #2 $175.63   7.285%   $188.4246   $188.42   $188.40   $188.40  
  Purchase #3 $55.45   9.295%   $60.6041   $60.60   $60.60   $60.60  
  Purchase #4 $203.77   7.625%   $219.3075   $219.31   $219.30   $219.30  
  Purchase #5 $212.87   9.355%   $232.784   $232.78   $232.80   $232.80  
  Purchase #6 $246.70   12.289%   $277.017   $277.02   $277.00   $277.00  
  Purchase #7 $225.55   6.503%   $240.2175   $240.22   $240.20   $240.20  
  7 purchase totals = $1,254.73       $1,365.9560   $1,365.95   $1,365.90   $1,365.90