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 $39.78   3.254%   $41.0744   $41.07   $41.05   $41.10  
  Purchase #2 $220.31   5.449%   $232.3147   $232.31   $232.30   $232.30  
  Purchase #3 $210.62   8.601%   $228.7354   $228.74   $228.75   $228.70  
  Purchase #4 $247.78   6.849%   $264.7505   $264.75   $264.75   $264.80  
  Purchase #5 $10.58   9.701%   $11.6064   $11.61   $11.60   $11.60  
  Purchase #6 $75.41   13.217%   $85.3769   $85.38   $85.40   $85.40  
  Purchase #7 $147.97   6.323%   $157.3261   $157.33   $157.35   $157.30  
  7 purchase totals = $952.45       $1,021.1844   $1,021.19   $1,021.20   $1,021.20