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 $216.98   13.202%   $245.6257   $245.63   $245.65   $245.60  
  Purchase #2 $35.84   9.141%   $39.1161   $39.12   $39.10   $39.10  
  Purchase #3 $138.97   6.482%   $147.978   $147.98   $148.00   $148.00  
  Purchase #4 $245.88   8.178%   $265.9881   $265.99   $266.00   $266.00  
  Purchase #5 $246.82   11.282%   $274.6662   $274.67   $274.65   $274.70  
  Purchase #6 $39.55   5.424%   $41.6952   $41.70   $41.70   $41.70  
  Purchase #7 $73.65   9.641%   $80.7506   $80.75   $80.75   $80.80  
  7 purchase totals = $997.69       $1,095.8199   $1,095.84   $1,095.85   $1,095.90