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 $162.75   8.407%   $176.4324   $176.43   $176.45   $176.40  
  Purchase #2 $118.68   11.740%   $132.613   $132.61   $132.60   $132.60  
  Purchase #3 $22.53   8.366%   $24.4149   $24.41   $24.40   $24.40  
  Purchase #4 $48.96   11.391%   $54.537   $54.54   $54.55   $54.50  
  Purchase #5 $60.34   5.613%   $63.7269   $63.73   $63.75   $63.70  
  Purchase #6 $217.92   5.595%   $230.1126   $230.11   $230.10   $230.10  
  Purchase #7 $216.57   8.780%   $235.5848   $235.58   $235.60   $235.60  
  7 purchase totals = $847.75       $917.4216   $917.41   $917.45   $917.30