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 $179.53   13.297%   $203.4021   $203.40   $203.40   $203.40  
  Purchase #2 $223.42   5.348%   $235.3685   $235.37   $235.35   $235.40  
  Purchase #3 $183.39   7.250%   $196.6858   $196.69   $196.70   $196.70  
  Purchase #4 $18.72   7.248%   $20.0768   $20.08   $20.10   $20.10  
  Purchase #5 $235.98   3.390%   $243.9797   $243.98   $244.00   $244.00  
  Purchase #6 $210.91   8.407%   $228.6412   $228.64   $228.65   $228.60  
  Purchase #7 $96.89   7.535%   $104.1907   $104.19   $104.20   $104.20  
  7 purchase totals = $1,148.84       $1,232.3448   $1,232.35   $1,232.40   $1,232.40