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 $187.47   6.803%   $200.2236   $200.22   $200.20   $200.20  
  Purchase #2 $227.60   11.199%   $253.0889   $253.09   $253.10   $253.10  
  Purchase #3 $160.55   3.701%   $166.492   $166.49   $166.50   $166.50  
  Purchase #4 $37.64   10.204%   $41.4808   $41.48   $41.50   $41.50  
  Purchase #5 $143.68   6.489%   $153.0034   $153.00   $153.00   $153.00  
  Purchase #6 $8.60   4.352%   $8.9743   $8.97   $8.95   $9.00  
  Purchase #7 $181.85   10.163%   $200.3314   $200.33   $200.35   $200.30  
  7 purchase totals = $947.39       $1,023.5944   $1,023.58   $1,023.60   $1,023.60