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 $132.62   12.446%   $149.1259   $149.13   $149.15   $149.10  
  Purchase #2 $23.48   9.303%   $25.6643   $25.66   $25.65   $25.70  
  Purchase #3 $174.42   12.654%   $196.4911   $196.49   $196.50   $196.50  
  Purchase #4 $85.29   6.511%   $90.8432   $90.84   $90.85   $90.80  
  Purchase #5 $172.66   11.453%   $192.4347   $192.43   $192.45   $192.40  
  Purchase #6 $83.60   8.769%   $90.9309   $90.93   $90.95   $90.90  
  Purchase #7 $201.34   12.408%   $226.3223   $226.32   $226.30   $226.30  
  7 purchase totals = $873.41       $971.8124   $971.80   $971.85   $971.70