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 $145.53   7.866%   $156.9774   $156.98   $157.00   $157.00  
  Purchase #2 $231.98   13.715%   $263.7961   $263.80   $263.80   $263.80  
  Purchase #3 $187.96   8.372%   $203.696   $203.70   $203.70   $203.70  
  Purchase #4 $55.57   4.227%   $57.9189   $57.92   $57.90   $57.90  
  Purchase #5 $76.84   11.274%   $85.5029   $85.50   $85.50   $85.50  
  Purchase #6 $151.29   7.633%   $162.838   $162.84   $162.85   $162.80  
  Purchase #7 $222.44   3.553%   $230.3433   $230.34   $230.35   $230.30  
  7 purchase totals = $1,071.61       $1,161.0726   $1,161.08   $1,161.10   $1,161.00