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 $62.55   5.830%   $66.1967   $66.20   $66.20   $66.20  
  Purchase #2 $74.48   6.453%   $79.2862   $79.29   $79.30   $79.30  
  Purchase #3 $196.98   6.414%   $209.6143   $209.61   $209.60   $209.60  
  Purchase #4 $51.57   8.825%   $56.1211   $56.12   $56.10   $56.10  
  Purchase #5 $31.58   6.519%   $33.6387   $33.64   $33.65   $33.60  
  Purchase #6 $227.60   8.320%   $246.5363   $246.54   $246.55   $246.50  
  Purchase #7 $11.81   5.598%   $12.4711   $12.47   $12.45   $12.50  
  7 purchase totals = $656.57       $703.8644   $703.87   $703.85   $703.80