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 $84.47   4.148%   $87.9738   $87.97   $87.95   $88.00  
  Purchase #2 $196.40   11.539%   $219.0626   $219.06   $219.05   $219.10  
  Purchase #3 $44.42   7.856%   $47.9096   $47.91   $47.90   $47.90  
  Purchase #4 $218.79   11.318%   $243.5527   $243.55   $243.55   $243.60  
  Purchase #5 $210.94   11.755%   $235.736   $235.74   $235.75   $235.70  
  Purchase #6 $232.88   9.868%   $255.8606   $255.86   $255.85   $255.90  
  Purchase #7 $17.57   6.731%   $18.7526   $18.75   $18.75   $18.80  
  7 purchase totals = $1,005.47       $1,108.8479   $1,108.84   $1,108.80   $1,109.00