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 $23.51   7.744%   $25.3306   $25.33   $25.35   $25.30  
  Purchase #2 $230.87   11.261%   $256.8683   $256.87   $256.85   $256.90  
  Purchase #3 $239.78   10.663%   $265.3477   $265.35   $265.35   $265.30  
  Purchase #4 $23.74   6.110%   $25.1905   $25.19   $25.20   $25.20  
  Purchase #5 $76.34   5.524%   $80.557   $80.56   $80.55   $80.60  
  Purchase #6 $204.44   4.147%   $212.9181   $212.92   $212.90   $212.90  
  Purchase #7 $172.65   12.429%   $194.1087   $194.11   $194.10   $194.10  
  7 purchase totals = $971.33       $1,060.3209   $1,060.33   $1,060.30   $1,060.30