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 $241.25   10.858%   $267.4449   $267.44   $267.45   $267.40  
  Purchase #2 $156.53   10.238%   $172.5555   $172.56   $172.55   $172.60  
  Purchase #3 $38.72   7.556%   $41.6457   $41.65   $41.65   $41.60  
  Purchase #4 $195.47   11.582%   $218.1093   $218.11   $218.10   $218.10  
  Purchase #5 $179.25   7.746%   $193.1347   $193.13   $193.15   $193.10  
  Purchase #6 $120.70   13.603%   $137.1188   $137.12   $137.10   $137.10  
  Purchase #7 $163.74   10.728%   $181.306   $181.31   $181.30   $181.30  
  7 purchase totals = $1,095.66       $1,211.3149   $1,211.32   $1,211.30   $1,211.20