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 $77.51   12.257%   $87.0104   $87.01   $87.00   $87.00  
  Purchase #2 $231.45   6.374%   $246.2026   $246.20   $246.20   $246.20  
  Purchase #3 $210.49   4.321%   $219.5853   $219.59   $219.60   $219.60  
  Purchase #4 $226.33   8.283%   $245.0769   $245.08   $245.10   $245.10  
  Purchase #5 $89.44   9.104%   $97.5826   $97.58   $97.60   $97.60  
  Purchase #6 $24.41   3.563%   $25.2797   $25.28   $25.30   $25.30  
  Purchase #7 $177.53   13.469%   $201.4415   $201.44   $201.45   $201.40  
  7 purchase totals = $1,037.16       $1,122.1790   $1,122.18   $1,122.25   $1,122.20