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 $41.76   9.136%   $45.5752   $45.58   $45.60   $45.60  
  Purchase #2 $133.75   5.839%   $141.5597   $141.56   $141.55   $141.60  
  Purchase #3 $225.39   12.696%   $254.0055   $254.01   $254.00   $254.00  
  Purchase #4 $181.54   11.639%   $202.6694   $202.67   $202.65   $202.70  
  Purchase #5 $123.52   8.547%   $134.0773   $134.08   $134.10   $134.10  
  Purchase #6 $193.79   3.702%   $200.9641   $200.96   $200.95   $201.00  
  Purchase #7 $45.88   3.841%   $47.6423   $47.64   $47.65   $47.60  
  7 purchase totals = $945.63       $1,026.4935   $1,026.50   $1,026.50   $1,026.60