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 $135.78   13.150%   $153.6351   $153.64   $153.65   $153.60  
  Purchase #2 $121.38   6.701%   $129.5137   $129.51   $129.50   $129.50  
  Purchase #3 $246.85   4.540%   $258.057   $258.06   $258.05   $258.10  
  Purchase #4 $41.89   5.280%   $44.1018   $44.10   $44.10   $44.10  
  Purchase #5 $64.43   11.585%   $71.8942   $71.89   $71.90   $71.90  
  Purchase #6 $184.82   11.280%   $205.6677   $205.67   $205.65   $205.70  
  Purchase #7 $150.76   12.228%   $169.1949   $169.19   $169.20   $169.20  
  7 purchase totals = $945.91       $1,032.0644   $1,032.06   $1,032.05   $1,032.10