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 $56.35   11.178%   $62.6488   $62.65   $62.65   $62.60  
  Purchase #2 $143.74   13.689%   $163.4166   $163.42   $163.40   $163.40  
  Purchase #3 $247.43   4.387%   $258.2848   $258.28   $258.30   $258.30  
  Purchase #4 $14.32   13.763%   $16.2909   $16.29   $16.30   $16.30  
  Purchase #5 $192.74   4.625%   $201.6542   $201.65   $201.65   $201.70  
  Purchase #6 $219.31   3.244%   $226.4244   $226.42   $226.40   $226.40  
  Purchase #7 $77.79   13.686%   $88.4363   $88.44   $88.45   $88.40  
  7 purchase totals = $951.68       $1,017.1560   $1,017.15   $1,017.15   $1,017.10