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 $57.61   12.780%   $64.9726   $64.97   $64.95   $65.00  
  Purchase #2 $233.39   13.246%   $264.3048   $264.30   $264.30   $264.30  
  Purchase #3 $110.32   11.259%   $122.7409   $122.74   $122.75   $122.70  
  Purchase #4 $231.64   8.509%   $251.3502   $251.35   $251.35   $251.40  
  Purchase #5 $187.55   12.797%   $211.5508   $211.55   $211.55   $211.60  
  Purchase #6 $177.40   5.786%   $187.6644   $187.66   $187.65   $187.70  
  Purchase #7 $170.38   6.401%   $181.286   $181.29   $181.30   $181.30  
  7 purchase totals = $1,168.29       $1,283.8697   $1,283.86   $1,283.85   $1,284.00