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 $91.71   8.276%   $99.2999   $99.30   $99.30   $99.30  
  Purchase #2 $241.51   11.533%   $269.3633   $269.36   $269.35   $269.40  
  Purchase #3 $243.58   8.736%   $264.8591   $264.86   $264.85   $264.90  
  Purchase #4 $92.99   13.585%   $105.6227   $105.62   $105.60   $105.60  
  Purchase #5 $55.26   8.723%   $60.0803   $60.08   $60.10   $60.10  
  Purchase #6 $171.47   9.391%   $187.5727   $187.57   $187.55   $187.60  
  Purchase #7 $72.35   6.646%   $77.1584   $77.16   $77.15   $77.20  
  7 purchase totals = $968.87       $1,063.9564   $1,063.95   $1,063.90   $1,064.10